[vtkusers] Scaling glyphs[Scanned]

Fri Apr 22 18:49:58 EDT 2005

Jim,

My preference, in the first instance, would be to improve or expand the
online documentation (header file). Some classes e.g. vtkAssignAttribute
contain example code fragments. I am sure that if you submitted
documentation changes in bite size chunks through http://www.vtk.org/Bug
it would be considered as a worthwhile and successful conclusion to a
discussion thread. However, I acknowledge that this is not a suitable
location for more general principals, techniques or workarounds, in
which case http://www.vtk.org/Wiki <http://www.vtk.org/Wiki/VTK_FAQ>
could be investigated.

John.

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
Behalf Of James C Robinson
Sent: 22 April 2005 11:04
To: 'John Platt'
Cc: Vtk Users
Subject: RE: [vtkusers] Scaling glyphs[Scanned]

John,

I wish I could get a copy of the tin... I am not the only one who feels
that VTK is underutilised because there isn't enough documentation. I
have the VTK book, but you simply won't get that kind of detail in it
(go on - make me out to be foolish by citing the page..). Even in the
online documentation there is only a cryptic indication of what the
relationship between ClampingOn and Scaling (everything is obvious in
retrospect). The route that the method names etc. indicate for toggling
between direction only and magnitude representation is the one I
originally took. You have to admit that it would take a deeper knowledge
to figure out your (John Biddiscombe's) elegant solution. Now, I have
encountered before the attitude that "nothing comes for free" and "you
have to make the effort" - it is almost "you have to pay your dues"
philosophy. However, that leads to a lot of replication of effort. The
users group is good and sometimes one can be successful in getting a
solution (as I have just experienced) - but not always (or even 50% of
the time). 

If there was somewhere to (easily) post the type of code I just wrote
(the three lines in my last e-mail) under the topic area of vtkGlyph3D
with the heading "Direction only vectors" or a number of indicative
titles that would allow an easy search - it would help us get mileage
out of all our efforts. This, of course, goes to "who organises it- on
what site?" and then gets into the area of Kitware's business model. I
would pay a few hundred dollars for a license for VTK to have such a
service. I am a middle level user (perhaps an overstatement of my
knowledge and ability) which means I am between the level whereby I can
justify (need to) paying $1000s for support (or development) or smart
guys who have a very in-depth knowledge (and thus need almost no
support).

There is a wide range of level of user and VTK would be even more
successful if it was better documented so that medium level users (such
as I might be) can use what is in the tin to its full potential.

Regards,

Jim

James C Robinson, 

*    42 Rivergrove,

         Glanmire,

         Co. Cork,

         Eire

'     +353 21 4822028

         +353 87 2393010

*    jrobinson at eircom.net> 

  _____  

From: John Platt [mailto:jcplatt at lineone.net] 
Sent: 22 April 2005 09:08
To: j.robinson at kepler-systems.com
Cc: vtkusers at vtk.org
Subject: RE: [vtkusers] Scaling glyphs[Scanned]

Hi Jim,

Flattery will get you everywhere :-) but credit to John Biddiscombe -
vtkGlyph3D does just what it says on the tin!

John.

-----Original Message-----
From: James C Robinson [mailto:j.robinson at kepler-systems.com] 
Sent: 21 April 2005 17:15
To: 'John Platt'
Cc: Vtk Users
Subject: RE: [vtkusers] Scaling glyphs[Scanned]

John,

Many thanks for your reply. Your solution will work (I think). I have
made a crude test and it behaves as desired. The subtlety is that, when
one wants an application that allows the toggling between two
representations of a vector field (scaled according to magnitude or not)
the simple way is to turn SetScaleModeToDataScalingOff). However, this
leads to the behaviour that wanted to avoid (source points outside the
field being represented). Using your approach means effectively that we
leave the SetScaleModeToDataScalingOn and when we want an orientation
only representation we set the clamping range to be very tiny (say
SetRange(0.0,minimum value). In this way all 0.0 magnitude vectors are
not represented and any others are shown the same size.

I hope this clarifies the clarification further. Again many thanks. It
is not necessary to always no the answer, but it really helps to know a
man/woman who does..

Jim

James C Robinson, 

*    42 Rivergrove,

         Glanmire,

         Co. Cork,

         Eire

'     +353 21 4822028

         +353 87 2393010

*    jrobinson at eircom.net> 

  _____  

From: John Platt [mailto:jcplatt at lineone.net] 
Sent: 20 April 2005 20:56
To: j.robinson at kepler-systems.com
Cc: vtkusers at vtk.org
Subject: RE: [vtkusers] Scaling glyphs[Scanned]

Hi Jim,

Have you tried ClampingOn() with ScalingOn(). Data scales outside the
clamp range are reset to the range end points. The data scale is then
normalized to the range 0 - 1. All glyphs with a data scale less than
the lower clamp range are therefore mapped to zero. Provided data
scaling is on (SetScaleModeToDataScalingOn()), the composite scale
factor, DataScale*ScaleFactor will also be zero.

HTH

John.

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
Behalf Of James C Robinson
Sent: 20 April 2005 13:46
To: Administrator
Cc: jcplatt at lineone.net
Subject: [vtkusers] Scaling glyphs[Scanned]

Dear all,

I am producing a set of glyphs using a vtkPlaneSource as the data
points. It works perfectly -  when I have scaling on, the glyphs behave
appropriately. However, when I turn scaling off (whowing vector
direction only) there are glyphs placed even at points (on the
vtkPlaneSource) that are outside the body (therefore magnitude is
implicitly zero).

I can Could anybody tell me if it is possible to have the glyphs
eliminated at points that are outside the field (or where the magnitude
is zero - or less than some threshold)?

Regards,

Jim

James C Robinson, 

*    42 Rivergrove,

         Glanmire,

         Co. Cork,

         Eire

'     +353 21 4822028

         +353 87 2393010

*    jrobinson at eircom.net> 

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